Many machine vision systems use a model of an object for locating and/or inspecting objects in an image.
In the field of semiconductor device manufacturing, a vacuum nozzle is used to pick up semiconductor chips. In manufacturing facilities using machine vision, it is sometimes necessary to inspect the nozzle to ensure that the nozzle will function reliably. To inspect the nozzle, an image of the nozzle is acquired by the machine vision system, and the image is searched with a model of the nozzle to find, and then inspect the nozzle.
It is known to use the Generalized Hough Transform (GHT), specialized to find circles, to create a GHT circular model of the nozzle, given the diameter of the nozzle. However, this approach can only find circular profiles of the nozzle that scale uniformly, and is therefore typically only used to find one ring or profile of the image of the nozzle, typically only the outer ring. Further, sometimes this approach does not provide sufficient accuracy regarding the position of the nozzle for some applications. Moreover, certain aspects of the relationship between the inner and outer profiles of the image of the nozzle cannot be inspected at all, such as concentricity, and bent nozzle conditions.